Conventionally this type of positioner is designed so as to operate with an electric current between 4 and 20 mA sent through a pair of electric wires from a higher-level system. For example, if a current of 4 mA is sent from the higher-level system, the valve opening of the valve is set to 0%, and if a current of 20 mA is sent, then the valve opening of the valve is set to 100%.
In this case, the supplied electric current from the higher-level system varies in the range of 4 mA (the lower limit electric current value) through 20 mA (the higher limit electric current value), and thus the internal circuitry within the positioner must operate on an electric current of no more than the 4 mA (for example, 3.8 mA) that can always be secured as an electric current value that is supplied from the higher-level system.
The opening setting value for the valve is inputted into the positioner by the higher-level system. Moreover, the actual opening value for the valve is obtained through the opening sensor. Consequently, the positioner is able to perform valve fault diagnostics, self-diagnostics, and the like, through performing calculations on the relationship between the opening setting value and the actual opening value for the valve. The provision of such fault diagnostic functions in the positioner makes it possible to increase the functionality of the system at a low cost, through eliminating the need for providing a separate fault diagnosing device (See, for example, Japanese Unexamined Patent Application Publication 2004-151941).
For reasons such as these, in recent years positioners have been provided with communication functions, self-diagnostic functions, valve diagnostic functions, valve opening output functions, and other added functions, in addition to the primary function (the valve control function (the basic function)) of controlling the opening of the valve.
However, even though there is a substantial improvement in high-functionality of the positioner through the incorporation of the added functions described above, there is the drawback that in order to exhibit all of these added functions, the electric current that is required increases as well If, in this case, the electric current that is supplied is insufficient for the electric current that is required in order to exhibit all of these added functions, the added functions will cease to operate properly, and, for example, there will be the risk of problems such as unidentifiable errors being sent continuously to the higher-level system, or communications with the higher-level system failing.
The examples of the present invention solve problems such as set forth above, and the object thereof is to provide a positioner that is able to exhibit high functionality, while ameliorating vulnerabilities when the electric current supply is inadequate.